(1) Field of the Invention
This invention generally relates to an underwater high speed projectile break screen based speed sensing circuit for the adaptable high speed underwater munition (AHSUM) project. More particularly, the invention relates to a sensing circuit for providing a state output of a break screen used in the testing of an underwater projectile. A resistive trace is placed in a plastic break screen. The resistive trace is coupled to a voltage divider and voltage comparator. Before the resistive trace is broken, a low signal is output from the comparator. When the resistive trace is broken, a high signal is output from the comparator. The comparator output is coupled to a programmable array logic (PAL) device which is configured to latch the high input signal and output the same for use by a data acquisition system.
(2) Description of the Prior Art
The known Adaptable High Speed Underwater Munition (ANSUM) project needed a method to sense the speed of underwater projectiles during the course of their test series, and particularly a calculation of the velocity of a projectile traveling at high rates of speed in an underwater firing range.
Previously, there was a need for a special material such as magnets in the projectile in order to obtain the necessary results. Thus, a problem exists in the art whereby there is a need for a break screen and sensing device which eliminates the need for special materials of the prior art.
The following patents, for example, disclose various types of break screens and velocity measuring systems, but do not disclose a device for sensing projectile velocity according to the aspects of the present invention.
U.S. Pat. No. 2,713,262 to Webster;
U.S. Pat. No. 3,656,056 to Dalzell, Jr.;
U.S. Pat. No. 3,792,354 to Slaght et al;
U.S. Pat. No. 4,128,761 to Oehler;
U.S. Pat. No. 4,845,690 to Oehler;
U.S. Pat. No. 5,349,853 to Oehler; and
U.S. Pat. No. 5,778,725 to Kirschner et al.
specifically, the patent to Webster discloses a method and apparatus for testing single samples of armor such as body armor. The ballistic apparatus and process of ballistic testing of the invention is designed to facilitate ballistic testing of armor specimens, to test single armor samples with a minimum of equipment, to yield comparative data between the test sample and aluminum or steel, and to yield information on the potential damage behind the armor plate. The ballistic apparatus and process reverses the usual laboratory procedure of firing a bullet at various velocities against a number of samples, and utilizes a gun shooting a bullet of known weight at a predetermined fixed velocity against a single unknown sample which is backed up by sheets of a standard material. In particular, the apparatus tests an armor plate with a projectile to determine the penetration resistance value of the armor plate to the projectile. The apparatus includes a plurality of centrally apertured frame members, means connecting the frame members in facing relationship with their central apertures in substantial registration, a test sample armor plate disposed between an end frame member and the next frame member, and a plurality of standard plates disposed between consecutive frame members from the next frame member.
The patent to Dalzell, Jr. discloses a resistance type of bullet hole locator in which the point at which a bullet or other passing object passed a line may be determined. Or, the direction from which the object came is ascertained by comparing the points at which the object passed spaced-apart lines or planes. Electrical resistance type elements, connected to an indicator or computer, indicate the points at which the object passed two or more lines or planes. As exemplary, one can determine the direction a bullet came from which struck a helicopter.
Slaght et al. discloses a system and method for determining the relative velocities of a projectile at different portions of its path in which a plurality of signaling detector stations are arranged at predetermined intervals along such path. A common receiving station is arranged to receive signals from the detector stations through a common communication channel. The receiving station has a memory unit capable of storing pulses corresponding to the signals received, and a calculator capable of analyzing adjacent pairs of the pulses which have been produced by passage of the projectile over two or more of the path intervals monitored by the detector stations. These features allow determination of the relative velocities of the projectile as it traverses the path intervals monitored by different pairs of detector stations. This information is used to study retardation properties of a projectile.
Oehler ""761 discloses a photodetector circuit for ballistic velocity measurement. Light perturbations sequentially produced by a projectile at spaced points are detected by photodetectors connected to a logarithmic diode circuit which is AC coupled to an amplifier time-shared by the detectors. Successive pulses from the amplifier are interpreted by logic circuits to start and stop an interval counter.
The ""690 patent to Oehler discloses a multiple screen ballistic chronograph. The chronograph system includes three shot-sensing screens which provide start and stop signals to interval-determining timers. The first screen provides a start signal to both timers and the subsequent screens provide stop signals to the first and second timers, respectively. The time intervals measured by these timers are divided into the distances between the screens to separately calculate two velocities based on two different distances. The calculated velocities are compared to evaluate the performance of the instrumentation so that measurement errors resulting from the instrumentation itself can be eliminated from analysis of the test shots.
The Oehler ""853 patent discloses an apparatus and method for measuring and calculating exterior and interior ballistics in a firearm. The apparatus includes a device for measuring pressure in a firearm-firing-chamber disposed at least in part at the strain sensitive region, and for producing analog signals indicative of the pressure, and connected to digitizing circuits which record the amplitudes of the signals representing pressure as a function of time; a plurality of muzzle bullet sensors for measuring the relative times at which the bullet passes the plane of each sensor and for producing analog signals indicative of these times, the analog signals being converted to digital signals and connected to digital timing circuits; and an acoustic target located downrange and including sensors arrayed at corners of a triangle for sensing acoustic energy emitted by a passing bullet and a device for generating analog signals representative of the acoustic energy sensed at the triangle corners.
The patent to Kirshner et al. discloses an assembly and method for testing an underwater gun. The test assembly is disposed in a tank of liquid and includes a mount for accepting and retaining the gun to be tested, a plurality of baffle plates, each having an aperture therethrough for alignment with a muzzle portion of the gun, a plurality of witness screens for alignment with the gun muzzle portion, a plurality of motion detection sensors for alignment with the apertures of the baffle plates, and a bullet receptacle for alignment with the gun muzzle portion for receiving a bullet fired from the gun. The device further contemplates a method for testing underwater guns, utilizing the assembly.
It should be understood that the present invention would in fact enhance the functionality of the above patents by providing a simplified device for sensing projectile velocity in an underwater environment in which each of at least two spaced break screen members are connected to a corresponding sensor, the sensor outputting a latched signal, and the latched signals being used to determine a velocity between the at least two spaced break screen members.
Therefore it is an object of this invention to provide a device for sensing projectile velocity.
Another object of this invention is to provide a device for sensing projectile velocity in an underwater environment.
Still another object of this invention is to provide a device for sensing projectile velocity in an underwater environment which utilizes a plurality of individually monitored break screens, each connected to a data acquisition system.
A still further object of the invention is to provide circuitry which is an accurate and inexpensive method to measure the velocity of a projectile under the water.
Yet another object of this invention is to provide a device for sensing projectile velocity in an underwater environment which is simple to manufacture and easy to use. In accordance with one aspect of this invention, there is provided a device for sensing projectile velocity in an underwater environment. The device includes a plurality of evenly spaced break screen members positioned in the path of a projectile. Each break screen member includes a support member, a pair of transparent sheets spanning the support member, a continuous resistive trace sandwiched between the transparent sheets, and a sensing member correspondingly connected to each resistive trace. The sensing member includes means for outputting a signal responsive to impact of the projectile against the break screen, and a logic arrangement for determining a difference between impact of two adjacent break screens throughout the run of break screens, thereby determining a velocity of the projectile.